1. Field of the Invention
The invention relates to a synthetic material, multifilament yarn. More particularly, the invention relates to synthetic material, multifilament yarn having good entanglement and good yarn quality that can be woven sizeless. Also presented is a method to make the yarn and a method of using the yarn. The yarn of this invention may be used in the fabric used to make air bags.
2. Description of the Related Art
The yarn used in the fabric for air bags is typically polyamide, either nylon 6 or nylon 66, polyester, polypropylene or polyethylene. Desirable qualities for air bag fabrics include: excellent tensile and tear strengths, high toughness and mechanical fatigue properties, high thermal stability, and appropriate air permeability. In addition, the yarn used to weave air bag fabric must yield a high pick per inch to ensure appropriate air permeability. Processability of the yarn used in weaving is important because it affects the final properties and the cost of the resultant fabric. A common problem with multifilament synthetic yarns during high speed weaving is the development of stripbacks which are the result of broken filaments in the warp yarns balling up (creating defects that are identified in the industry as stripbacks, fuzzballs, slubs, etc.), which can result in breakouts due to the negative affect on the fill. Such breakouts reduce the efficiency of weaving and increase costs. To reduce such problems, methods to increase the cohesiveness of multifilament synthetic yarns have been typically pursued.
One method is to apply sizing to the yarn. Sizing is the procedure wherein the yarn is coated with a substance (e.g. polyacrylic acid, polyvinyl alcohol, polystyrene, polyacetates, wax, oil, gelatin, starch, etc.) to bind the filaments of the yarn together and to stiffen the yarn to provide abrasion resistance during weaving. The process of applying sizing is commonly called "slashing" in the industry. Abrasion reduction contributes to a reduction in the number of breaks, stripbacks, fuzzballs, etc. during the course of weaving. Such problems can significantly reduce productivity in the weaving process if encountered frequently. Disadvantageously, however, the use of sizing requires several extra steps in the fabrication process. In addition, it also involves extra cost to purchase sizing and to dispose of the removed sizing after weaving. The elimination of the need for the use of sizing would represent a significant improvement.
Another method for providing cohesion between the filaments is the use of what is known variously as entangling, mingling, commingling, or interlacing. The term "entangling" will be used herein for convenience but the other terms could just as easily be substituted therefor. Entangling is a process which forms a series of intermittent sections along the length of the yarn wherein the individual filaments are tightly entangled with each other. These entangled sections are known variously as entanglements, nips, nodes or knots and are separated from each other by lengths of filaments wherein the individual filaments are relatively parallel to each other. The entanglements act to prevent the individual filaments from spreading and splaying during processing of the yarn, thereby maintaining a cohesive yarn bundle. Entangling alone however is often not sufficient to provide a yarn which can be reliably woven sizeless for air bag fabrics and similar fabrics, using current weaving looms with the desired efficiency.
Entangled yarns are known in the art. Commonly-assigned U.S. Pat. No. 5,434,003 teaches a yarn having an entanglement strength of at least about 4.5, an entanglement strength coefficient of variance of less than about 1.10 and an average entanglement length for each entanglement of at least about 11.0 mm. The yarn has a knitting performance of at least 4,000 racks/defect. The yarn of this patent is intended for knitting, not for weaving. The patent is silent on the yarn quality. Commercially available entangled yarns include AlliedSignal's 1R86 nylon 6 yarn and Akzo's 447HRT nylon 6 yarn.
Prior art teachings to produce a sizeless yarn are also known. U.S. Pat. No. 5,657,798 teaches a yarn having a mean opening length of from 2 to 10 cm, and the coefficient K1 for the stability of the intermingling points of the yarn exceeds 0.6 and the coefficient K2 for the stability of the intermingling points of the yarn exceeds 0.3. This patent is silent on the yarn quality. Other relevant teachings include U.S. Pat. No. 5,518,814. An on-line yarn quality detection device is taught for example in U.S. Pat. No. 5,718,854.
Therefore, there is no description in the prior art of yarn having both good entanglement and good yarn quality which can be woven sizeless, nor a process for producing such a desirable yarn.